Perhaps picky, but there is no such thing as a winter rated 30 weight oil which is what 30w would stand for. But we knew you really meant 30 weight oil------not 30w.
The reason air cooled engine manufacturers often recommend a dine 30 weight oil is that a 10w-30 dino oil will shear down to a 10w-25 or 10w-20 oil after a few hours of use. That could be too thin to lube the engine when under heavy load and in a warm ambient. Their marketing people don't want to burden their customers with a multi-weight synthetic oi (that won't shear down) because of the added expense.
Choosing a good synthetic oil with a multi-vis rating will provide easy starting and quick lube after a start. Meanwhile the higher weight viscosity won't shear down and continue to provide good lube when the engine is hot.
My sons had a commercial lawn mowing business to pay their college expenses. They had 61" and 72" mowers with Kohler air-cooled engines and I used Mobil 1 15w-50 oil in them. I kept the 72" mower when they quit the business and got "real" jobs. It has over 3000 hours on it and running fine.
Besides the 15w-50 oil, Mobil also has a 5w-40 turbo diesel oil that is also rated for spark engine use. Either would be a good choice or similar viscosity from a reputable supplier. Read that to mean Shell, Amoco etc. but not "boutique" brands like Amsoil, Red Line etc.
Mark
2000 Itasca Suncruiser 35U on a Ford chassis, 80,000 miles
2003 Ford Explorer toad with Ready Brake supplemental brakes,
Ready Brute tow bar, and Demco base plate.
